#include <iostream>
#include <cstdio>
#include <cstdlib>

using namespace std;

#define MAX_N 100
long long arr[MAX_N + 5] = {0};
long long f(int n) {
    if (n <= 2) return n;
    if (arr[n]) return arr[n];
    arr[n] = f(n - 1) + f(n - 2);
    return arr[n];
}

int main() {
    int n;
    cin >> n;
    cout << f(n) << endl;
    return 0;
}